Solid propellant composition containing carboxy-terminated polymers



United States Patent 3,532,566 SOLID PROPELLANT COMPOSITION CONTAININGCARBOXY-TERMINATED POLYMERS Hyman R. Lubowitz, Pasadena, Charles Kuchar,Glendora, Harold L. Greenberg, West Covina, and Raymond M. Price,Glendora, Califi, assignors to Aerojet- General Corporation, Azusa,Calif., a corporation of Ohio No Drawing. Filed Nov. 29, 1962, Ser. No.241,058 Int. Cl. C06d /00 US. Cl. 149-19 9 Claims ABSTRACT OF THEDISCLOSURE High energy propellant compositions are produced by reactinga liquid carboxy-terminated polymeric adduct with a curing agent and anoxidizer. The curing can be accomplished at room temperature to producea solid propellant free of internal stresses at normal temperatures. Thepolymeric adduct is formed from individual units containing an aromaticnucleus and a halogen.

This invention relates to novel curable polymeric adducts and solidpropellants having as the binder such adducts.

In the preparation of propellant formulations it is desirable that thebinder material be in the liquid state prior to the incorporation of theoxidizer and other additives into the binder. This makes for greatlyincreased ease of incorporation and handling as compared with bindermaterials which are rubbery prior to curing.

Previously it has been a problem in the propellant art to obtain abinder material which though liquid prior to curing, would cure to arubbery elastomer at low temperatures, in the order of room temperatureor below. For example, it has been proposed that a liquid polybutadienecontaining two carboxyl terminal groups be used as the liquid bindermaterial. However, this binder material must be cured at a temperatureof around 130 to 150 F. These relatively high curing temperatures haveseveral disadvantages. For example, many of the newer oxidizer materialssuch as hydrazine perchlorate are not stable for prolonged periods atthese high curing temperatures. Thus, the propellants compounded fromsuch oxidizers, using the known liquid binder materials, are notcompletely satisfactory. Further, the liquid binder materials previouslyknown which are curable only at higher temperatures, possess otherserious disadvantages. 'Ihus, such high temperature curing materialstend to shrink upon cooling after the cure has been carried out. Thisshrinkage in the propellant sets up stresses which can produce cracks inthe grain. These may result in motor failure during firing due to asudden increase in the burning area when the faces of the cracks areexposed.

An additional problem in the propellant art has been to provide a firmlyadherent liner material for the motor casing. Normally, a highly filledpropellant composition will not satisfactorily adhere to the metalrocket casing. For this reason, various liner materials have beenproposed to form an adhesive bond between the casing and the propellantmaterial. Previous liner materials have not been sufficiently adherentfor this purpose, and thus have tended to pull away from the casing.Lining defects of this type can cause motor failure or unduly rapidburning due to the increased burning surface.

It is an object of this invention to prepare new liquid polymericadducts which can be cured at room temperatures or below. It is anotherobject of this invention to employ these liquid polymeric materials toobtain highly 3,532,566 Patented Oct. 6, 1970 r' ICC loaded propellantcompositions. It is still another object of this invention to preparesolid propellant compositions from the novel liquid binder materialswhich are substantially free of internal stresses.

In still another aspect of this invention, it is an object to prepare anew cured polymer which will adhere to both a propellant grain and themotor casing, thus being useful as a motor liner. These and otherobjects of our invention will be apparent in the detailed descriptionwhich follows.

It has now been found that certain new liquid carboxyterminated polymeradducts are suitable as binders in castable propellant compositions. Thepropellant batches containing these liquid polymeric materials can besimply poured into forms and cured at room temperature or below toobtain a solid propellant which is substantially free of internalstresses at normal temperatures. The liquidity of the batch prior tocuring greatly simplifies handling of the mass.

It has further been found that the new liquid carboxyterminated polymersof this invention can be blended with large amounts of solids withoutthe expenditure of large amounts of mechanical energy in the mixingprocess. These liquid polymers therefore permit of the addition of largeamounts of solids in less time.

The new cured polymers have demonstrated a high degree of adherence tometals and solid propellant, and thus have been found to yield superiormotor liners.

The new liquid carboxy-terminated polymeric adducts of this inventionhave the following generic formula:

wherein X is a halogen selected from the group consistmg of fluorine,chlorine, bromine and iodine, n is an integer of from 1 to 4, and m isan integer having the value 2 or 3. When In in the above formula has avalue of 2, R is a polymeric divalent organic radical selected fromthose having the formula:

such as ethylene, propylene or butylene, and r is an integer having avalue of from about 20 to about 200;

and

wherein R is selected from the group consisting of hydrogen and methyl,and p is an integer having a value of from about 12 to about 120. When mis 3 in the above formula, R is a trivalent aliphatic organic radical ofthe wherein A is a lower alkylene radical, containing from 1 to about 4carbon atoms, r is an integer of from about 8 to about 75, and R is astraight or branched chain trivalent alkylene radical having from 3 toabout 8 carbon atoms such as with one mole, for every hydroxy equivalentin said polyol, of an aromatic acid anhydride having the formula:

wherein R, X, m and n are as defined above.

The polyols employed in the preparation of the abovementioned liquidpolymers are diols such as polyethylene glycol polyethylene ether,poluypropylene ether glycol, poly-1,2-butylene ether glycol,polytetramethylene ether glycol, polyisoprene glycol and polybutadieneglycol; and triols such as the adducts obtained by the reaction ofalkylene oxides such as ethylene oxide, propylene oxide, butylene oxide,tetrahydrofuran and mixtures thereof, with aliphatic trihydroxycompounds such as glycerine, trimethylolpropane and 1,2,6-hexane triol.

Typical suitable acid anhydrides of the above formula are materials suchas monochlorophthalic anhydride, monobromophthalic anhydride,tetrafluorophthalic anhydride, chloroendic anhydride, andtetrachlorophthalic anhydride. It has been found that the use of theabovementioned acid anhydrides are essential to the obtention of aliquid polymer which is curable at room temperature or below. Thus, ifnon-halogenated acid anhydrides are employed, it has been found that thecuring temperature rises to a level which is undesirable. Similarly, ifan organic dibasic acid such as terephthalic acid or adipic acid is usedin lieu of the above-mentioned anhydrides for reaction with the triols,the preparation of acidterminated polymers is unsatisfactory because ofthe formation of highly viscous or gel-like materials which are whollyunsuitable for the production of unsuitable propellants. Further, theuse of such dibasic acids is also unsatisfactory with the foregoingdiols because there results a product containing a multiplicity ofmaterials of varying molecular weight. In fact, the product includessome unreacted dibasic acid which cannot be readily separated. Thisdisparity in molecular weight of the various components in the productprevents the formation of a uniform and complete cure.

The preparation of the liquid polymers of the above formula is carriedout at a temperature of from about 80 C. to about 150 C. Normally, thereaction is most conveniently carried out under atmospheric pressure. Ifdesired, the reaction between the polyol and the acid anhydride may beassisted by the use of a small amount of a catalyst such as triethylenediamine. Optionally, the reaction may be carried out in the presence ofan inert organic solvent such as benzene or toluene. In general, as hasbeen pointed out above, the polyol and acid anhydride are employed instoichiometric amounts, but other proportions may be used.

During the preparation of the liquid carboxy-termi nated polymer, it isfrequently desirable to agitate the medium so as to improve the contactbetween the reactants. The finished polymer is isolated in conventionalmanner by stripping, filtration and/0r evaporation.

The Examples which follow are for purpose of illustration only, andshould not be regarded as limitative in any way. Except as otherwiseindicated, percentages are by weight.

EXAMPLE I Preparation of liquid carboxy-terminated polymer A typicalpreparation of the novel liquid carboxy-terminated polymer of thisinvention is as follows:

Into a three-necked 3-liter round bottom flask fitted with a stirrer,reflux condenser and thermometer, the following materials were charged:

0.30 mole of a triol having a molecular weight of about 4500 andprepared by reacting one mole of 1,2,6- hexane triol with about moles ofpropylene oxide (this material may be obtained from the Union CarbideChemical Company under the trade name LAT-42); 2.16 grams oftriethylenediamine, and 300 grams of benzene. The mixture was heatedwith stirring at 120 C. for one hour during which time refluxing benzenedehydrated the mixture by entraining water into a separatory funnel.After the mixture had cooled to 65 C., 0.90 mole of tetrachlorophthalicanhydride was added. The mixture was then again heated under reflux to115-120 C. for two hours. After cooling to ambient temperature, thebenzene was removed and the solution was placed under vacuum of 2-5 ml.mercury. The solution was then heated to l15120 C. and maintained undervacuum for one hour. After filtering, a pale orange liquidcarboxy-terminated polymer was obtained.

The above example was repeated using polybutadiene glycol instead of thetriol. A liquid carboxy-terminated polymer was obtained.

When the foregoing procedure was repeated using mono-chlorophthalicanhydride in lieu of tetrachlorophthalic anhydride and polypropyleneether glycol in lieu of the above-mentioned triol, similar results wereobtained.

EXAMPLE II Following the procedure set forth in the preceding Example,one mole of polytetramethylene ether glycol having a molecular weight of3000 is reacted with two moles of tetrachlorophthalic anhydride inbenzene solution. The reaction is carried out for about one hour atl001l0 C. A liquid, carboXy-terminated polymeric adduct is obtained.

EXAMPLE III One mole of polyethylene glycol, having a molecular Weightof about 2000, [a compound wherein in the above formula R is (CH isreacted with two moles of tetrabromophthalic anhydride in accordancewith the procedure set forth in Example I. A liquid, carboxy-terminatedpolymeric is obtained in good yield.

EXAMPLE IV One mole of the reaction product of one mole of glycerin with30 moles of propylene oxide is reacted with three moles ofmonofluorophthalic anhydride in toluene solution for 12 hours at C. Afluorine-containing, carboxy-terminated adduct is obtained.

The novel liquid carboxy-terminated polymers of this invention can becured, in the absence or presence of fillers or other additaments, totough elastomers at room temperature or below by aziridinyl curingagents.

These aziridinyl curing agents may be, for example, of the followingformulae:

Ra Z a. an

L \CH Ra Ra H(J $11 NAsN HC/ \JIH I i; 1&4

and

Be an (")-N l H la R3 R3 11 z i z JH a J M/ 110/ \CH It, I

wherein in the above formulae, Z is oxygen or sulfur, R and R arehydrogen or lower alkyl, R is lower alkyl or phenyl, and A is analkylene radical of from 1 to about carbon atoms. The lower alkyl groupscontain from 1 to about 4 carbon atoms and include methyl, ethyl, propyland butyl. Illustrative of such compounds are tris(methylaziridinyl)phosphine oxide, bis(methyl aziridinyl)phenylphosphine oxide,N,N,N,N-diethyleneurea, N,N,N,N-diethylenethiourea,l,4-bis-(-l-azirdnyl)- butane, l,l0-bis-(-l-aziridinyl)decaneN,N,N,N,N",N"- triethylene trimesicamide, and tris(aziridinyl)phosphinesulfide. Other curing agents can be used where the low curingtemperature is less critical, as in the forming of motor liners. 'Forexample, the liquid polymers of this invention can be cured at 100F.-l10 F. by epoxy curing agents such as3,4-epoxy-6-methylcyclohexylmethyl- 3,4-epoxy-6-methyl cyclohexanecarboxylate, the reaction product of 3 moles of epichlorohydrin with onemole of para aminophenol, or epoxidized polybutadiene having a molecularweight within the range from about 800 to about 9000. Even at 100110 F.,the cure temperature of our polymers with epoxies is far below the 180F. temperature used to epoxy-cure previously known car'- boxy-terminatedpolybutadienes.

EXAMPLE V Cure of liquid polymer When 1.8 grams of tris-(methylaziridinyl)phosphine oxide and 40 grams of mica are blended with 38.2grams of the liquid carboxy-terminated polymer, prepared in Example II,and maintained at room temperature for several hours, a tough curedrubber is obtained.

The cured rubber has a wide variety of uses. Thus, rubbers of this typefind application in electrical wire insulation, tank linings, cements,hoses and belting.

The novel liquid carboxy-terminated polymers, containing a curing agentand other additives, can be cured to a solid product at room temperatureor below, or at higher temperatures, if desired. Normally, curing iscarried out at a temperature of from about 40 F. to about F. It is to beunderstood that curing can be carried out at higher temperaturesalthough such is not necessary and, as has been pointed out above, issometimes un desirable.

Propellants may be prepared from our novel liquid polymers by theinterblending of an oxidizer and the curing agent, followed by curing. Awide variety of solid oxidizers may be combined with our polymers.Typical of suitable inorganic oxidizers are the alkali metal andalkaline earth metal perchlorates, chlorates, nitrates, chromates,dichromates and permangantes. Illustrative of such oxidizers are lithiumperchlorate, potassium perchlorate, calcium perchlorate, potassiumchlorate, calcium chlorate, potassium chromate, potassium dichromate,potassium nitrate, lithium nitrate, potassium permanganate and calciumnitrate. Likewise, ammonium salts of the above-mentioned anions can beused such as ammonium perchlorate, ammonium nitrate, ammonium dichromateand ammonium permanganate. Still another suitable inorganic oxidizer ishydrazine perchlorate. Illustrative of the organic oxidizers suitable inthe practice of this inventon are cellulose nitrate and guandinenitrate.

In general the propellant compositions of our invention comprise:

liquid polymer--about 5 to about 40 parts by weight per 100 parts oftotal propellant composition,

oxidizer-about 40 to about parts by weight per parts of total propellantcomposition,

curing agentan effective amount in the order of about 0.5 to about 20parts by weight per 100 parts of total propellant composition,

With any desired additional ingredients being present in the balance ofthe composition which can include combustion addtives, fillers,stabilizers, plasticizers, etc.

More preferably, the propellant composition comprises:

liquid polymerabout 5 to 20 parts by weight per 100 parts of totalpropellant composition,

oxidizerabout 65 to about 72 parts by weight per 100 parts of totalpropellant composition,

curing agentabout 0.5 to about 10 parts by weight per 100 parts of totalpropellant composition.

Combustion additives such as the powdered metals, i.e., powderedaluminum, powdered beryllium, etc., may also be added to the propellantcompositions of this invention. The preferred powdered metals are thosehaving an average particle size of 2528 microns. These powdered metalcombustion additives serve to increase the specific impulse of theresulting propellant. These combustion additives are generallyadvantageously employed in an amount of from about 25 to about 200.parts by weight for each 100 parts of the liquid polymer used in theformulation. Preferred of our propellants are those in Which the amountof oxidizer plus combustion additive constitutes about 75 to about 90percent by weight of the total propellant composition with thepropellant having an oxygen balance of about zero to about -60,calculated on the basis of total conversion of the carbon, hydrogen andmetal in the propellant to carbon dioxide, water and metal oxide,respectively.

The propellant compositions of this invention may contain optionally, inaddition to the above-mentioned ingredients, other additaments such aswetting agents, stabilizers, fillers, plasticizers, and processing aids.

Thus, there may be added to the propellant composition prior to curingfrom about to about 50 parts by weight of a plasticizer per 100 parts ofliquid polymer. Typical plasticizers are materials such as hydrocarbonoils, fluorinated plasticizers, waxes, asphalts, higher aliphatic andaromatic esters and resins such as hydrogenated ester gums. Preferredplasticizers are isodecyl perlargonate and the nitro-plasticizersdisclosed in assignees copending US. Pat. application, Ser. No. 2,072,filed .Tan. 12, 1960.

The propellant interblending procedure to be followed in the practice ofour invention is as follows: a liquid polymer, as defined above, isadded to an internal mixer and is degassed. Then the wetting agents,stabilizers, fillers, processing aids, plasticizers and combustionadditives are added to the polymer and mixed for a period of timenecessary for their incorporation into the polymer. The oxidizer, ororidizers, are then added in increments and mixed under vacuum. Afterall the oxidizer has been incorporated, the curative is added and mixedunder vacuum until it is incorporated. The mixture is then cast,preferably under vacuum, from the mixer into containers. Manymodifications of this procedure are possible. Thus, the liquid polymerand the plasticizer may be added simultaneously to the mixer.

The mixer which we have found to be particularly effective forinterblending our propellant ingredients is that known commercially asthe P mixer. The P mixer is manufactured by Baker-Perkins, Inc., ofSaginaw, Mich., and it can be equipped with facilities for heating,cooling, and vacuumizing propellant batches during mixing.

EXAMPLE VI To a mixer which was maintained at about 70 F. was added 9.1parts of a liquid carboxy-terminated polymer prepared from aolytetramethylene ether glycol having a molecular weight of about 3000and tetrachlorophthalic anhydride in accordance with the procedure setforth in Example II. Then parts of bis-(2,2-dinitropropyl) formal and 20parts of aluminum powder having an average particle size of 25 to 28microns were added. These ingredients mixed until the aluminum wascompletely wetted down. The mixture was then degassed under vacuum forabout 10 minutes, then 60 parts of ammonium perchlorate was added andmixing continued for about 20 minutes. Then 0.9 part of tris(methylaziridinyl)phosphine oxide was added as a curing agent and mixingcontinued for an additional 5 minutes. During this time the temperaturewas maintained at about 70 F. The mixture was then cast and cured at 80F. for 16 hours. The resultant product was rubbery.

When the above example was repeated, using hydrazine perchlorate in lieuof the ammonium perchlorate, as the oxidizer, a satisfactory rubberypolymer was again obtained after curing for 16 hours at 80 F.

EMMPLE VII Following the procedure set forth in Example VI, 21propellant was prepared from the following ingredients:

Ingredient: Weight percent Carboxy-terminated polymer frompolytetramethylene ether glycol having a molecular weight of about 3000and tetrachloro- A resilient polymer was achieved after curing for 16hours at 80 F.

The motor liner compositions of this invention normally contain thefollowing ingredients in the percentages indicated:

liquid polymerabout 5 to about parts by weight per parts of total linercomposition,

curing agent-an effective amount in the order of about 0.5 to about 20parts by weight per 100 parts of total liner composition,

fil1ers0 to about 60 parts by weight per 100 parts of total linercomposition.

In addition, this liner composition may contain plasticizers,stabilizers and other additives well-known in the rubber art. Preferredfillers are materials such as titanium dioxide and mica.

The following examples illustrate the use of the polymers of thisinvention in a motor liner material.

EXAMPLE VIII A sandblasted steel motor casing was coated with a liquidcomposition consisting of 80 parts by weight of a carboxy-terminatedpolymer (prepared in accordance with the process described above byreacting one mole of a 1,2,6-hexane triolpropylene oxide adduct having amolecular weight of 4500 with three moles of chlorendic anhydride); 10parts of 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexane carboxylate and 10 parts oftitanium dioxide. The coated casing was cured for 3 days at F. Thecoated casing was then filled with a polyurethane propellant prepared inaccordance with assignees copending U.S. application, Ser. No. 33,054,filed May 31, 1960; from 65 parts ammonium perchlorate, 17 partspowdered aluminum, 2 parts polytetramethylene ether glycol, 3.2 partsneopentyl glycol azelate, 6.2 parts polypropylene ether glycol, 0.055part triethanol amine, 4.24 parts isodecyl pelargonate, 0.1 part carbonblack, 0.1 part sulfur, 0.35 part copper chromite, 1 part toluenediisocyanate, 0.10 part lecithin and 0.06 part ferric acetylacetonate.The propellant was then cured for three days at F. The coating was foundto adhere tenaciously to both the casing and the propellant.

The following coatings were also found to have good adherence to boththe propellant and the casing.

EXAMPLE IX Ingredient: Weight percent Polytetramethylene etherdiol-tetrachlorophthalic anhydride adduct (prepared according to ExampleII) 85.97 Tris(methylaziridinyl)phosphine oxide 3.98 Titanium dioxide10.00 Phenylbetanaphthylamine 0.05

EXAMPLE X Ingredient:

Polytetramethylene ether diol-tetrachlorophthalic anhydride adduct(prepared according to Example II) 81.18

Reaction product of 3 moles epichlorohydrin and one mole paraaminophenol 8.82

Titanium dioxide 10.00

EXAMPLE XI Ingredient:

Polypropylene ether glycol-tetrachlorophthalic anhydride adduct(prepared according to Example I) 81.54

Epoxidized polybutadiene MW-2000 8.46

Titanium dioxide 10.00

It will be understood that various modifications may be made in thisinvention without departing from the spirit thereof or the scope of theappended claims.

9 I claim: 1. A high energy propellant composition comprising thereaction product of a liquid carboxy-terminated polymeric adduct havingthe generic formula (I ll-H O m wherein X is a halogen, small n is aninteger of from 1 to 4, small m is an integer of from 2 to 3; whereinwhen when m has a value of 2, R is a polymeric divalent organic radicalselected from those having the formula wherein q is an integer having avalue from about 60 to about 600,

wherein A is a lower alkylene radical and r is an integer having a valuefrom 20 to about 200, and

D wherein R is selected from the group consisting of hydrogen and methyland p is an integer having a value of from about 12 to about 120; andwherein when m is 3, R is a trivalent radical of the formula l A \L .1/3

wherein A is a lower alkylene radical and r is an integer having a valueof from about 8 to about 75, and R is a trivalent alkylene radical; andabout 0.5 to about 20 parts of a curing agent per 100 parts ofpropellant, and about 40 to about 90 parts of an oxidizer per 100 partsof propellant, said propellant having an oxygen balance of from about 0to about 60.

2. The composition of claim 1 wherein the oxidizer is ammoniumperchlorate.

3. The composition of claim 2 wherein the oxidizer is hydrazineperchlorate.

4. The composition of claim 3 wherein there is present a powdered metalcombustion additive in an amount of from about 25 parts to about 200parts by weight for each 100 parts of liquid carboxy-terminated polymer.

5. The method of preparing a propellant composition which comprisesinterblending about to about 40 parts by weight per 100 parts ofpropellant of a liquid carboxyterminated polymeric adduct having theformula wherein X is a halogen, n is an integer of from 1 to 4, m is aninteger of from 2 to 3; wherein when in has a value of 2, R is apolymeric divalent organic radical selected from those having theformula wherein q is an integer having a value from about to about 600,

wherein A is a lower alkylene radical and r is an integer having a valuefrom about 20 to about 200, and

wherein A is a lower alkylene radical, r is an integer having a value offrom about 8 to about 75, and R is a trivalent alkylene radical, withabout 0.5 to about 5 parts of a curing agent per 100 parts ofpropellant, and about 40 to about parts of an oxidizer per parts ofpropellant, and permitting the interblended mixture to cure.

6. The method of claim 5 wherein the curing .is effected at roomtemperature.

7. The method of claim 6 wherein the oxidizer is ammonium perchlorate.

8. The method of claim 7 wherein the oxidizer is hydrazine perchlorate.

9. The method of claim 8 wherein there is present a powdered metalcombustion additive in an amount from about 25 parts to about 200 partsper 100 parts of the carboxy-terminated polymer.

References Cited UNITED STATES PATENTS 2,970,128 1/1961 Csendes 26041.52,880,191 3/1959 Newton 260-415 3,038,872 6/1962 Wolf 26041.5 3,050,4238/1962 Hudson 149-19 3,087,844 4/1963 Hudson et a1. l49l9 OTHERREFERENCES Chem. & Eng. News, Aug. 8, 1960, p. 53, 149-19. Chem. & Eng.News, Aug. 1, 1960, p. 35, 149-19.

BENJAMIN R. PADGETT, Primary Examiner U.S. Cl. X.R. l4936, 42

